In-process accumulation systems such as for use in manufacturing assembly lines in general must have immediate recovery capabilities. That is, in the event the loading of articles ceases for a period of time less than the accumulation time, then the accumulator can recover its inventory and maintain the supply of articles to the unload device without interruption. Prior methods of in-process accumulation or inventory can be divided into two modes of operation; namely, synchronous and non-synchronous, both of which are well known in the manufacturing industries.
Synchronous accumulators generally employ a multi-function load device and multiple mechanisms to store and transfer parts or articles. The load device may have the ability to load either into the accumulator or directly into the unload station or unload device. Consequently, in the event the load device ceases to load parts or articles, the synchronous accumulator reverses its cycle and continues to supply parts to the unload station or device. One example of this is a vertical accumulator or stacker. The disadvantages of such an accumulator or stacker is in the cost of the multiple mechanisms required and non-independence of the load and unload devices; that is, the accumulation system must be operated according to the slowest work station and timing of the other work operations depends upon the slowest station. Further, there is no way in which work can be piled up ahead of a work station that may be temporarily out of order. That is, all of the work pieces or articles are moved simultaneously and intermittently by the conveyor.
Non-synchronous accumulators do allow for the random movement of parts within the accumulator. The load and unload stations can operate totally independent of each other without regard to cycle time. The articles used in this type of accumulator generally must be transferred as by pallets or mass accumulated on a conventional, continuous moving conveyor such as a chain, belt or similar conveyor or stacked in a first in, first out queue. Disadvantages of non-synchronous accumulators is that they require costly fixed pallets which may be returned to the load station or the articles must be limited to a geometric shape which can be independently moved in an oriented stable fashion. In some such conveyors pallets which carry the work pieces or articles are clutched to and declutched from a continuously moving conveyor chain. Successive pallets can be stacked up behind any given station by being declutched from the chain until space in the station becomes available. The problem with this type of system is that the backup pallets tend to be expensive. The clutching and declutching devices are prone to wear out and shock absorbing devices are required to absorb the stress of sudden clutching and declutching.
In an article conveyor system it is desirable to utilize the advantages of both synchronous and non-synchronous accumulation systems. That is, the conveyor system should provide both the storage and transfer of articles from a load station to an unloading station particularly in an automated assembly line. The total system should provide for combining the use of totally independent and dedicated robotic load and unload devices of non-similar cycle times yet has immediate recovery capabilities.
By this invention an accumulator and transfer system is provided which accomplishes the above desired qualities.